The prior art most closely related to that of the present invention is that covered by U.S. Pat. No. 5,328,309 (Bishop et al), U.S. Pat. No. 5,292,214 (Bishop et al) and U.S. Pat. No. 5,390,408 (Bishop et al). These prior art references relate to "slotting machines" which machine the slots in the bore of power steering valve sleeves. The design of these machines calls for each of the slots to be scooped out of the bore of a turned blank by a finger-like cutting tool mounted on a cutting spindle which angularly reciprocates about an axis in a series of progressively deeper cutting and return strokes so forming a (usually) closed chamber, or hydraulic port, which is arcuate in longitudinal section. The sleeve is held in a work holding collet, in turn mounted in a work holding spindle, having a rotational axis perpendicular to and offset with respect to the cutting spindle axis. By accurately indexing the work holding spindle upon completion of each slot, the required number of slots are precisely machined in the sleeve, usually 4, 6 or 8 slots for most automotive applications.
Such prior art slotting machines have always been arranged to form each slot longitudinally in the bore surface, which is at the time of cutting furthest from the cutting spindle axis. In view of this and having regard to the arcuate path of the cutting tool during each cutting stroke, the slot has necessarily had a concave floor. This has limited the nature and configuration of the slots that have been able to be formed. The concave slots typically used have been blind-ended, but in some designs the concave slots exit from either or both axial extremities of the sleeve bore surface to provide for oil return from the sleeve.
It has been found that the aforesaid limitations on slot configuration have imposed limitations on design of steering gear valves and an object of the invention is to alleviate that situation.